The present invention relates to a method for recycling organic thermoplastic values, such as polycarbonate values from discarded organic thermoplastic substrates which have been surface treated with an organic or organosilicon material. More particularly, the present invention relates to a method for effecting the removal of a protective or decorative organic, or organosilicon coating including the removal of surface impregnated organic or organosilicon material, such as an organic UV stabilizer from various discarded organic thermoplastic substrates which can be in granular form, by treating the organic thermoplastic substrate with an aqueous alkaline solution, recovering the resulting treated organic thermoplastic substrate and thereafter washing and drying such organic thermoplastic substrate.
Organic thermoplastic substrates and particularly polycarbonate substrates are often used in glazing applications. Shaped organic thermoplastic substrates often employ a protective coating to preserve optical clarity and impact resistance. In applications not requiring optical clarity, organic thermoplastics nevertheless often use a protective coating to avoid scratch marks and/or to minimize environmental degradation, particularly if the organic thermoplastic substrate such as a polycarbonate article is used in outdoor applications.
One procedure used in treating polycarbonate sheet can involve the use of a silicone hardcoat (SHC), where the polycarbonate sheet is dipped into the hardcoat formulation and thereafter the treated polycarbonate sheet is dried followed by the thermal curing of the silicone resin. Additional protective coatings commonly used on polycarbonate articles are acrylic hardcoats and hardcoats based on formaldehyde-melamine resins (FMR). Other organic thermoplastics, such as a polymethylmethacrylate sheet can be initially treated with a thermoset acrylic primer followed by the application of a silicone hardcoat.
Organic thermoplastic end users and organic thermoplastic manufacturers such as found in the polycarbonate industry, have been faced with environmental concerns due to the build-up of discarded organic thermoplastic articles surface treated to improve scratch resistance and resistance to weathering. Surface treated organic thermoplastic articles often deteriorate after an extended period of time under atmospheric conditions, such as at least 6 months; scrap polycarbonate material also can be generated during the initial treatment of polycarbonate sheet with a silicone hardcoat formulation as a result of drips, runs, sags or dust inclusions which can mar the finish. The treated polycarbonate sheet is often discarded because it cannot be recycled. It is often disposed of by landfilling which can create environmental concerns.
Several studies have been made with respect to the removal of protective or decorative coatings from organic thermoplastics such as polycarbonates. Some of the procedures which have been used include, sandblasting, radio frequency heating, ice jet blasting, melt filtration, cryofracturing, high pressure water jet and grinding with wire brushes. Although such techniques have been found effective for removing hardcoat to a significant extent from the surface of various organic thermoplastic substrates, the resulting organic thermoplastic substrates in most instances, are often different in impact resistance and opacity as compared to the original virgin organic thermoplastic substrate. With respect to wire brushing, although effective in particular instances, it has been found limited to flat surface substrates having certain minimal dimension requirements.
It would be desirable therefore to provide a method which would allow salvaging of organic thermoplastic values, such as polycarbonate values, from surface treated polycarbonate articles, which normally would be discarded to minimize environmental concerns. It also would be desirable to be able to reclaim such organic thermoplastic values from such surface treated organic thermoplastic substrates to permit the direct blending of such salvaged values with virgin organic resin to provide organic thermoplastic articles having substantially the same optical clarity and impact resistance as parts made from the virgin resin.